It is often useful or desirable to cool devices and materials. For example, focal plane arrays and other instruments can often benefit from or require cooling to cryogenic (e.g. 10 Kelvin or less) temperatures. Systems for cooling devices and materials to cryogenic temperatures have required significant amounts of power, are heavy, and complex. In a typical cryocooler, a Stirling cryocooler is used to pre-cool gaseous helium to approximately 17 K. The gaseous helium is then used in a Joule-Thomson expansion to achieve temperatures between 4K to 10 K. Operation of such systems can, for example, require 414 W of electrical power to achieve 65 mW of heat lift at 10 K. The weight of a typical implementation of such a system is 45 kg. Accordingly, it is difficult and expensive to operate or to deploy such systems in remote environments, including but not limited to space or on-orbit environments. As a result, such cryocoolers have typically been limited to use in laboratories.
Other techniques for cooling devices and materials include expanding liquid hydrogen into a gas. However, the temperature that can be achieved by expanding liquid hydrogen has usually been limited to no less than 15 K. Moreover, this technique results in the consumption of the liquid hydrogen, which often is unacceptable in the context of the requirements of a given mission or application.